1. Field of the Invention
The present invention relates to a control system of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, in the past, the fuel used has mainly been fossil fuels. However, in this case, burning such fuels produces CO2, which causes global warming. On the other hand, burning ammonia does not produce CO2 at all. Thus, there is known an internal combustion engine made so as to use ammonia as fuel and not produce CO2 (for example, see Japanese Patent Publication (A) No. 5-332152.).
However, ammonia is harder to burn compared with fossil fuels. Therefore, when using ammonia as fuel, some sort of measure is required for making the ammonia easier to burn. Thus, in the above-mentioned internal combustion engine, exhaust heat is utilized to reform the ammonia so as to produce reformed gas comprised of hydrogen and nitrogen, the hydrogen in the produced reformed gas is stored in a hydrogen storing alloy, and the hydrogen stored in the hydrogen storing alloy is fed together with the ammonia in a combustion chamber so as to enable easier combustion even when using ammonia as fuel.
In this regard, CO2 is not produced even if burning ammonia as explained above. However, if burning ammonia, N2O exerting an influence upon global warming is produced. In this case, however, when an exhaust purification catalyst arranged in an engine exhaust passage is activated and the air-fuel ratio of exhaust gas in the exhaust purification catalyst is the stoichiometric air-fuel ratio or rich, the N2O produced in a combustion chamber is reduced in the exhaust purification catalyst. Accordingly, at this time, almost no N2O is discharged into the atmosphere.
Contrary to this, when the inside of the exhaust purification catalyst becomes a state of excessive oxygen, that is, a lean state, almost no N2O is reduced in the exhaust purification catalyst. Accordingly, the risk arises that the N2O will be discharged into the atmosphere. Further, when the exhaust purification catalyst is not activated as well, almost no N2O is reduced in the exhaust purification catalyst. Accordingly, in this case as well, there is a risk that N2O will be discharged into the atmosphere.
The present invention is to provide a control system of an internal combustion engine suppressing discharge of N2O into the atmosphere.
In a first aspect of the invention, there is provided a control system of an internal combustion engine using as a fuel a first fuel of ammonia and a second fuel which is easier to burn than ammonia and feeding these two types of fuel into a combustion chamber to burn, wherein a reference ammonia ratio indicating a ratio of an amount of ammonia fed to a total amount of fuels fed is set in advance in accordance with an operating state of the engine, an ammonia ratio is usually set to the reference ammonia ratio in accordance with the operating state of the engine, and the ammonia ratio is temporarily made lower than the reference ammonia ratio in accordance with the operating state of the engine at the time when feed of the fuels is restarted after feed of the fuels is suspended at the time of deceleration.
In a second aspect of the invention, there is provided a control system of an internal combustion engine using as a fuel a first fuel of ammonia and a second fuel which is easier to burn than ammonia and feeding these two types of fuels into a combustion chamber to burn, wherein the fuels are injected toward an interior of an intake port of each cylinder so that normally, an injection is completed before opening of a corresponding intake valve and, at the time when feed of the fuels is restarted after feed of the fuels is suspended at the time of deceleration, an air-fuel ratio is temporarily made rich and an injection action of the fuel is carried out for at least a cylinder to which the fuel should be fed first even when an injection end timing of the fuel is during opening of an intake valve.
In a third aspect of the invention, there is provided a control system of an internal combustion engine using as a fuel a first fuel of ammonia and a second fuel which is easier to burn than ammonia and feeding these two types of fuels into a combustion chamber to burn, wherein a reference ammonia ratio indicating a ratio of an amount of ammonia fed to a total amount of fuels fed is set in advance in accordance with an operating state of the engine, an ammonia ratio is normally set to the reference ammonia ratio in accordance with the operating state of the engine, and the ammonia ratio is made lower than the reference ammonia ratio in accordance with the operating state of the engine at the time when a temperature of an exhaust purification catalyst arranged in an engine exhaust passage is lower than a predetermined set temperature.
In an engine, when feed of the fuels is restarted after feed of the fuels is suspended at the time of deceleration, the interior of the exhaust purification catalyst has become a lean state. Accordingly, at this time, if N2O is produced in a combustion chamber, the N2O is discharged into the atmosphere. Accordingly, in the first aspect of the invention, at this time, the ammonia ratio is lowered so that the amount of production of N2O is suppressed, while in the second aspect of the invention, the air-fuel ratio of the exhaust gas in the exhaust purification catalyst is made the stoichiometric air-fuel ratio or rich at an early stage so that the amount of discharge of N2O into the atmosphere is suppressed. Further, in the third aspect of the invention, when the exhaust purification catalyst is not activated, the ammonia ratio is lowered so that the amount of production of N2O is suppressed.